Advances in microelectronics technology tend to develop device chips which occupy less physical space while performing more electronic functions. Conventionally, the chips are packaged for use in housings which protect the chip from its environment and provide means for input/output communication between the chip and external circuitry. The continuing drive toward miniaturization thus results in generation of more heat in less physical space with less structure for removing the heat from the package. Similarly, the development of electronic circuit device chips using compound semiconductors further expands the requirements for packaging which can contain devices operating at higher temperatures and control device temperatures by heat dissipation.
In many device packages heat conduction from the chip to the exterior of the package is accomplished by a high thermal conductivity transfer medium which is in thermal communication with the chip and has a dissipation surface adjacent the surface of the package. Other packages merely conduct the heat through the package itself. However, in order to dissipate heat from the package, an external heat sink must be attached to the device package. Typically, the heat sink is a body of material such as metal which has a high thermal conductivity. The heat sink ordinarily has at least one flat face for positioning adjacent a face of the device package and may include fins, pins or other structures for dissipating thermal energy into the surrounding atmosphere.
To be effective, the heat sink must occupy as little space as possible while dissipating maximum amounts of thermal energy. It is also desirable that the heat sink be readily attachable to and removeable from the device package and adaptable for connection to a wide variety of different device packages. Where large numbers of the devices are used in an assembly process, economics demand that the assembly process, including assembly of heat sinks, etc., be simple, automatable, versatile and reliable. Accordingly, attaching heat sinks by adhesives, screws, bolts and the like is highly undesirable. Attachment by simple clips and the like is much preferred because it is fast and usually very easy.
Previous attempts to secure a heat sink to a chip or chip housing tend to reduce the amount of potential heat dissipation surface area and do not fixedly secure the heat sink. Typical examples are disclosed in U.S. Pat. No. 5,208,731 to Blomquist entitled Heat Dissipating Assembly and Japan Patent No. 71154 to Koga entitled Method of Mounting Heat Sink. In Koga and Blomquist the attachment consists of a snap-on clip and the force needed to install the clips must be applied in the plane of the heat sink between the pins or fins of the heat sink, thereby risking damage to the heat sink pins or fins. Furthermore, the attachment assembly is not secured to the heat sink. Accordingly, when the heat sink is removed from the chip housing, the clip is a loose part and a potential hazard if dropped. In addition, the arrangements disclosed in the aforementioned patents preclude preassembly of the heat sink and attachment. Instead, assembly of the attachment to the heat sink must be performed simultaneously with the installation of the circuit device. Accordingly, there is a need for an improved heat sink attachment assembly which can be fixed to the heat sink before installation on the device package and one which reduces the risk of damage to the heat sink and device package during the installation procedure. Furthermore, an attachment assembly is needed which occupies minimal space so that the heat dissipation properties of the heat sink configuration are not adversely affected.